1. Field of the Invention
The present invention relates to an angular velocity sensor for detecting an angular velocity by utilizing occurrence of a Coriolis force corresponding to the angular velocity of rotation of a vibrator in a direction perpendicular to a vibrating direction of the vibrator when the vibrating vibrator is rotated.
2. Related Background Art
Since a mechanical rotating top rate gyroscope is large and expensive, there has been developed an angular velocity sensor for public use as called as a piezoelectric gyroscope or oscillation gyroscope which is effective in power savings, longer in life, and suitable for decrease in size.
FIG. 1 is a perspective view to show a conventional angular velocity sensor comprising such an oscillation gyroscope. A vibration piece for detection 4 is mounted through a coupling member 3 above a vibration piece 2 fixed on a base 1, while a vibration piece for detection 7 is mounted through a coupling member 6 above a vibration piece 5 similarly. There are provided on the vibration piece 2 a piezoelectric element drive 8 vibrating the vibration piece 2 in the X-direction and a piezoelectric element for monitor 9 for monitoring actual vibrations of the vibration piece 2. Also, a piezoelectric element detector 10 is provided on the vibration piece for detection 4 to detect vibrations in the Y-direction. Similarly, a piezoelectric element drive 11 and a piezoelectric element monitor 12 are provided on the vibration piece 5, and a piezoelectric element detector 13 is on the vibration piece for detection 7.
In the above arrangement, while the vibration pieces 2, 5 are vibrating at a resonance frequency .omega.1 with a constant amplitude as opposing to each other in the X-direction, and when the vibration pieces 2, 5 are rotated together with the base 1 at an angular velocity .OMEGA. about the Z-axis, a Coriolis force Fc proportional to the angular velocity .OMEGA. acts on the vibration pieces for detection 4, 7 to vibrate the vibration pieces for detection 4, 7 at the resonance frequency .omega.1. Since an amplitude of the vibrations of the vibration pieces for detection 4, 7 is proportional to the angular velocity .OMEGA., the angular velocity .OMEGA. may be obtained by detecting the amplitude of the vibrations by the piezoelectric elements for detection 10, 13. In the detection, in order to keep the amplitude of the vibration pieces 2, 5 constant, the amplitude is detected by the piezoelectric elements monitor 9, 12 and the detected amplitude is fed back to each drive signal of the piezoelectric element drives 8, 11.
The above-described conventional example, However, includes a drawback of an inability of increase in detection precision of angular velocity because the resonance frequency would be deviated and the attenuation property would be distributed unless the work and assembly precision of the vibration pieces 2, 5 and the vibration pieces for detection 4, 7 should be high. In addition, since the parts are not integrally made, the assembly becomes complicated and the sensor cannot be made smaller or cheaper.
An angular velocity sensor free of the above drawbacks was proposed in Japanese Laid-open Patent Application No. 61-139719. FIG. 2 is an exploded perspective view to show a construction of the angular velocity sensor as disclosed. In FIG. 2, reference numeral 51 designates a substrate made of silicon, 52 a spacer, and 53 a support substrate made of silicon. A cantilever beam 50 is formed on the substrate 51 by etching. An electrode 54 is provided at a free end of the cantilever beam 50. An AC signal is applied from a generator 55 to the electrode 54 to vibrate the free end of the cantilever beam 50 in the Z-direction.
In FIG. 2, when the substrate 51 rotates about the Y-axis, the free end of the cantilever 50 is vibrated by a Coriolis force in the X-direction. Since an amplitude of the vibrations in the X-direction corresponds to an angular velocity of rotation, the angular velocity may be measured by detecting the vibrations by piezo resistance elements 56a and 56b mounted on the cantilever beam.
There appears, however, a force to vibrate the fixed end as a reaction to the vibrations at the free end in the arrangement of FIG. 2. This force is absorbed by a material of the substrate, and, therefore, the vibrations of the free end are attenuated by an amount as absorbed. Thus, the angular velocity sensor of FIG. 2 is not effective to generate the vibrations in the Z-direction, and has a loss in vibrations in the X-direction, resulting in a decrease in detectivity.